Toán Lớp 7: tìm x : (1/2 +3x).(x^2 – 4/9) + 0 x^2 là x mũ 2

Question

Toán Lớp 7: tìm x : (1/2 +3x).(x^2 – 4/9) + 0
x^2 là x mũ 2, hướng dẫn giải giúp em bài này ạ, em cảm ơn thầy cô và các bạn nhiều.

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Thúy Hường 6 tháng 2022-05-25T20:43:40+00:00 2 Answers 0 views 0

TRẢ LỜI ( 2 )

  1. Answer
    (1/2 + 3x) . (x^{2} – 4/9) = 0
    $\Rightarrow$ $\left[\begin{matrix} \dfrac{1}{2}+3x=0\\ x^2 – \dfrac{4}{9}=0\end{matrix}\right.$
    $\Rightarrow$ $\left[\begin{matrix} 3x=0-\dfrac{1}{2}\\ x^2 =0+\dfrac{4}{9}\end{matrix}\right.$
    $\Rightarrow$ $\left[\begin{matrix} 3x=\dfrac{-1}{2}\\ x^2 =\dfrac{4}{9}\end{matrix}\right.$
    $\Rightarrow$ $\left[\begin{matrix} x=\dfrac{-1}{2}:3\\ x^2 =(\pm\dfrac{2}{3})^2\end{matrix}\right.$
    $\Rightarrow$ $\left[\begin{matrix} x=\dfrac{-1}{6}\\ x=\pm\dfrac{2}{3}\end{matrix}\right.$
    $\text{Vậy}$ x \in {-1/6 ; 2/3 ; -2/3}
     

  2. $\text{($\frac{1}{2}$+3x).(x²-$\frac{4}{9}$)=0 }$
    $\text{⇔\(\left[ \begin{array}{l}\frac{1}{2}+3x=0\\x²-\frac{4}{9} =0\end{array} \right.\) }$
    $\text{⇔\(\left[ \begin{array}{l}x=$\frac{-1}{2}$ \\x²=$\frac{4}{9}\end{array} \right.\) }$
    $\text{⇔\(\left[ \begin{array}{l}x=$\frac{-1}{2}$ \\x²=(\frac{2}{3})² \end{array} \right.\) }$
    $\text{⇔\(\left[ \begin{array}{l}x=$\frac{-1}{2}$ \\x=$\frac{2}{3}$\end{array} \right.\)}$
    $\text{Vậy x ∈ {$\frac{-1}{2}$ hoặc  $\frac{2}{3}$}$

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